Wow that was hard, I seem to know what my top 4 are but it is hard to decide the other 6 because you have to debate within yourself which one should get your vote.
I agree with bibliophile that a re watch is worth our time especially the first three seasons. My question has always been what if we had kept some of the characters that we threw away so easily how would that have changed the show and would it have brought some new energy, I am thinking like Merlin, Hades, Mr. Hyde or used barely used characters in a more productive way Leroy, Jefferson (I know he had better things), Grace, Archie, Nova, etc. Instead of Henry having a relationship with a girl we did not know and really did not care about how about Grace which could have been built as a slow friendship and small crush. I think that would have been better. Merlin was a very charismatic character and I think OUAT could have done SO much with him if they kept him around the same with Hades and Hyde.